The use of microRNA's (miRNA) for the study, detection, prognosis and cure of disease is growing and becoming a reliable tool toward improving human health. In this regard the immune system is an important area since T cells are greatly impacted by deletion of dicer a key RNA processing enzyme required for the generation of miRNA. To gain new insight into how miRNA impact T cell responses, mice were immunized with costimulation and adjuvant to generate potent T effector responses. We generated a cDNA library that could trace changes in miRNA derived from lymphoid tissue. Using sequencing of size-fractionated cDNA we cloned 6 potential miRNAs from this library and found candidates that possessed characteristic stem loop folding and were dicer dependent. One of these candidates, termed miR-R89, was unique compared to the others since its expression was hematopoietic specific and also regulated during immune activation. The targets and function of miR-R89 are currently unknown but our new preliminary data show that it is expressed in a T cell clone known to cause experimental autoimmune encephalitis (EAE). In Aim 1 we will use a powerful proteomic strategy to examine the effects of blocking miR-R89 on the T cell proteome followed by our bioinformatics gene targeting data and a molecular approach to validate potential target genes. In Aim 2 we will study how miR-R89 inhibition affects the initiation and progression of EAE. Thus, this R21 proposal will explore how a new miRNA can impact specific T cell function, which may lead to a novel translational approach for multiple sclerosis in humans. PUBLIC HEALTH RELEVANCE: This application will characterize the immune and therapeutic potential of a small RNA we cloned, which may be able to control gene expression of important pathways that impact immune T cell activation. This notion will be tested in a mouse model of Multiple Sclerosis (MS) with the hope of developing more efficient therapy for MS patients. Our work will bring fresh insight into the field and add greatly to the control of immune gene expression in the immune system by microRNA.